This trial will evaluate the safety and efficacy of losigamone in the treatment of patients with complex partial seizures in whom: (1) an optimal losigamone dosage has been determined and (2) the previous antiepileptic drug (AED) has been discontinued (patients may present with simple partial seizures in addition to complex partial seizures). After an 8-week losigamone monotherapy baseline period, patients will be randomized under double-blind conditions to either: (1) continue their optimal losigamone dosage or (2) titrate to one-half the optimal losigamone dosage and will enter an 8-week treatment period. Efficacy will be assessed by the variable time-from-randomization-to-meeting-exit criteria. Safety will be evaluated by comparing the nature and duration of the adverse experiences. The trial will be conducted at multiple epilepsy centers.